The present invention relates to axle supporting rods, such as radius rods and stabilizers, used in suspension systems of motor vehicles.
Stabilizers are generally used as a type of axle supporting rods for stabilizing the posture of the body of motor vehicles in rolling motion.
A conventional stabilizer is a rod bent in a predetermined shape, and consisting of a torsion section and a pair of arm sections extending the ends of the torsion section. When is used in a motor vehicle, the torsion section is positioned extending in the transverse direction of the vehicle, while the arm sections are coupled at their free ends to a pair of suspension systems of the vehicle.
In a typical prior art example, the free ends of the arm sections are flattened and have a fitting hole.
The ends of the conventional stabilizer can be shaped with relative ease by forging or the like. In a stabilizer of this type, however, the ends are restricted to a uniform shape and cannot be varied. Therefore, the stabilizer is not adaptable to a variety of suspension systems.
In a prior art stabilizer of another type, coupling members, manufactured independently of the arm sections, are welded to the end of the arm sections. Although this stabilizer can be fitted with coupling members of various shapes, it is subject to the following drawbacks.
In welding the coupling members to the arm sections, rapid heating or cooling of welds will cause various malfunctions. In order to avoid this, it is absolutely necessary to perform both preheating and postheating before and after welding Thus, welding the coupling members requires many processes and facilities, resulting in an increase in cost.
These days, in particular, stabilizers tend to be used under severe stress conditions. Accordingly, spring steel with a high carbon equivalent is commonly used as a material for the stabilizers. Welding the spring steel, however, involves several problems. The aforesaid preheating and postheating would, for example, require precise control of temperature and time.
Stabilizers of yet another type have a function as tension rods, in addition to their primary function as stabilizers.
The body of stabilizers of this type is selected to tension on its arm sections, as well as both bending and torsional moment. Each arm section has a thread formed at its end whereby the arm section is coupled to the suspension system.
Stabilizers these days tend to be hollow for reduced motor vehicle weight and economy of resources. Hollow stabilizers, however, have not yet been put to practical use as stabilizers doubling as tension rods. One of the reasons for this is that even though pipes can be used for the torsion section and arm sections in view of their mechanical strength, no effective or reliable coupling means for connecting the stabilizer body and the coupling members at the ends of the body has yet been developed.
In a prior art system disclosed in Japanese Utility Model Publication No. 55-153207, solid coupling members are fixed to a hollow stabilizer body by fitting the former into the ends of the latter. In this case, however, the coupling members are limited in fixing strength and are not very high in reliability. Accordingly, conventional stabilizers are integrally formed from a solid material, having thread portions at their ends. In this case, however, the stabilizer body is heavy in weight. Also, the stabilizer body and the thread portions are integral with one another so that it is difficult to form the thread by rolling. Thus, threading inevitably requires cutting work, resulting in increased cost.
The stabilizer doubling as a tension rod is expected to have an accurate length in the longitudinal direction of the motor vehicle. If the stabilizer body is formed integrally with the portions, however, it is impossible to correct distortion caused by heat treatment. It is, therefore, difficult for the stabilizer body to have specified dimensions.
Prior art radius rods will now be described. Radius rods are rods which serve to determine the longitudinal position of an axle, and to counter torque produced at the time of acceleration or deceleration of a motor vehicle. See JASO (Japanese Automobile Standards Organization), 3006 radius rod systems.
Most of the prior art radius rods are straight and low in working stress. Conventionally, therefore, carbon steel for mechanical structures (equivalent to S30C provided by Japanese Industrial Standards), or other low-carbon steel is frequently used as a material for the radius rods. Where low-carbon steel is used for radius rods, the rod-shaped radius rod body can be welded to the coupling members without any problem.
Recently, however, there has been an increasing demand for radius rods whose bodies are partially bent for reasons of accomodating the layout of particular suspension systems.
Radius rods of this type are used under severer stress conditions than straight radius rods. Consequently, the use of low-carbon steel for their material provides insufficient strength. Thus, it is necessary to use spring steel to form the radius rod, treating the spring steel with heat for higher tensile strength.
However, because of its high carbon equivalent, the spring steel cannot easily be welded, as in the case of the radius rods described above.